364 



BIOLOGY OF THE LABORATORY MOUSE 



Infection of the primary host occurs by ingesting the infected inter- 

 mediate host. The cysticercoid which has developed in the intermediate 

 host is Hberated in the intestine of its new host and within 18 days it has 

 become attached to the epitheUum of the intestine and has developed into an 

 adult worm. 



Control measures might profitably be directed toward eliminating any 

 fleas which might be living as parasites on the animals and also toward keep- 

 ing the feed room or bins free from meal worms, the 

 larvae of the Tenebrio beetle. 



Hymenolepis microstoma (dujardin, 1845). — This 

 species of mouse and rat tapeworm (Fig. 143C) 

 probably occurs much more rarely than the other two 

 species of Hymenolepis that have been described, but it 

 is an interesting form in that the adult is not limited to 

 the intestine. The adults live in the duodenum and 

 the common bile duct which, as described by Joyeux 

 and Kobozieff (24), in intense infestation may be 

 distended until it is as large as the duodenum. The 

 gall bladder also may be completely filled. 



Joyeux and Kobozieff (24) have given a complete 

 description of the adult worm. The measurements 

 which they give are: length 80 mm. to 350 mm.; 

 breadth of scolex 200 n; breadth of rostellum 100 ju; 

 neck 600 IX from base of scolex to first sign of segmenta- 

 tion. There is a simple corona of 27 hooks. 

 Development occurs in several insects, notably in the 

 Tenebrio and in the rat flea, Nosopsyllus fasciatus. 



Dobrovolskaia-Zavadskaia and Kobozieff (10) 

 have described lesions produced by the parasites in 

 the liver and bile ducts. If the ductus choledocus is heavily infected, its wall 

 becomes chronically inflamed and irregularly thickened, and the mucous 

 membrane becomes hyperplastic. However, they state that the hyperplasia 

 of the mucous membrane has never presented a neoplastic character. When 

 the parasite penetrates the liver, it causes destruction of the parenchymatous 

 cells and focal necrosis. In more advanced cases large abscesses develop. 



Fig. 145. — Head 

 and anterior portion 

 of H. diminuta from 

 the rat. (Enlarged.) 

 {From Stiles and 

 Crane, after Zschokke.) 



Nematodes 



Many species of nematodes have been reported as parasites of the house 

 mouse. However, a number of these probably seldom would be of impor- 



